As is known in the art, polyacrylamide is in general a white, solid polymer having a relatively high molecular weight and has the formula (CH.sub.2 CHCONH.sub.2) and is useful in a variety of industries. For example, in its dry state, it is useful in earth filled dams, in conjunction with bentonite, to prevent seepage of water. In addition, it has been utilized in drilling muds, again in conjunction with expanding lattice clays such as bentonite. Since polyacrylamide, in these industries, and others, is utilized as a dry solid it is, in general, desirable if when the polymer is produced it is in the form of a dry solid polymer which does not need further processing to be used per se except, perhaps, grinding the solid into a smaller particle size.
As noted, if a polymer is to be utilized in the dry form it is desirable to produce that polymer in the same form as it is to be used. It is therefore not surprising that certain workers in the art have attempted to produce dry polymer of acrylic acid wherein the polymer is in the dry form. Patents that may be mentioned are U.S. Pat. Nos. 2,833,745; 2,956,046; and 3,058,958. These patents deal primarily with producing dry salts of acrylic resins and, in general, are not applicable to polyacrylamide polymers and, moreover, the methods disclosed in these patents are relatively complicated and inefficient.
For example, U.S. Pat. No. 3,058,958 discloses a method for polymerization of acrylic salts as a thin film. The patent discloses a very complicated method in that rollers are provided which are driven in opposite directions and the polymerization solution drips onto the rolls. The polymerization solution itself is an aqueous solution of calcium acrylate, sodium acrylate, and an initiator. According to the patent the calcium acrylate increases the effective polymerization rate. The initiator is in the same solution as the sodium and calcium acrylate and the solution is not preheated which is essential in the present invention.
U.S. Pat. No. 2,956,046 discloses a very complicated method of producing dry acrylic acid polymers by spray polymerization thereof. The aqueous dispersion of sodium acrylate in a catalyst is dispersed into heated air having a temperature of 350.degree. F. to 400.degree. F. which, as noted above, is very inefficient and, moreover, could not be used in the instant process.
U.S. Pat. No. 2,833,745 discloses a process for producing sodium polyacrylate in which the critical portion of the patent apparently resides in the fact that the initiator must be added during the evolution of carbon dioxide. As is readily apparent this is a complicated method of producing a dry salt and moreover is not applicable to producing polyacrylamide.